The invention relates to a method for processing organic material and, particularly to a method, which utilizes highly ammoniacal organic material in cleaning a biogas produced in degradation, and to equipment for implementing the method. The invention also relates to products obtained by the method.
The publication U.S. Pat. No. 4,824,571 discloses a method and equipment for degradation of various organic products and wastes in an anaerobic medium. The method generates degraded products and biogas. In the method the mass to be degraded is introduced into a fermentation vat and the produced biogas is recovered. Thereafter the biogas is fed back into the vat from the bottom so as to provide a fluidization effect.
The publication U.S. Pat. No. 4,302,236 discloses a use of a composting system for scrubbing gas effluvia. In the method, inorganic acid-forming constituents are removed from a gas stream high in sulphur, in particular. Inorganic groups form inorganic acids in the presence of oxygen or water. The gas stream to be cleaned is passed through an active composting biodegradable organic waste, which is held under thermophilic bacteria-phase digestion conditions.
The publication WO 93/06 064 discloses a method for neutralizing and recovering gases formed in connection with wet composting. The object of the invention described in the publication is to render harmful, toxic and/or polluting manure gases harmless. According to the publication part of the gases is recycled to the composted mass so as to improve its nutrient value.
The publication DE 3,134,980 discloses a method for mixing biomass in oxygen-free environment in a biogas reactor by means of biogas produced by bacterial strains and stored in a biogas storage. In the method the biomass is mixed with periodic biogas blows. The necessary biogas pressure is provided by means of the bacterial strains in the biogas reactor. The reactor is externally closed and it communicates with the biogas pressure vessel. Pressure is released in the biogas pressure vessel and next it is blown into the biomass, from which the biogas is further conducted into a biogas container.
EP application 486,466 discloses a method for controlled and continuous aerobic biological decomposition of organic wastes. Decomposing material, which is optionally inoculated with a mixture of bacteria and microbes, is fed into the material in the microbiological waste and the degraded material is removed, whereby an oxygen-containing gas is passed in for the degradation. The aim of the method described in the publication is to control the degradation of nitrogen-containing products. In the method, CO2 gas is added to the oxygen-containing gas, depending on the NH3 content and the pH of the degradation product, whereby the gas is mixed with a fraction that contains no, or very little, nitrogen. The method described in the publication is an aerobic method.
Organic material is received from various sources from products of plant and animal origins. One problem with organic material degradation plants is that availability of material to be processed is season-dependent and within a short period of time the plant must be able to process even large amounts of organic matter solids, because they do not allow long storage. Preservation of organic material poses several problems, for instance, preservation produces NH3, which is a toxic compound and prevents microbes from functioning. Currently the bioconversion reactors allow introduction of only low solids contents, because NH3 prevents the microbial function in the reactors. Preservation of seasonally produced organic material also causes problems, because it cannot be preserved neither in acidic nor in basic conditions, if conventional bioconversion processes are employed, because they are sensitive to variations in the pH. Conventional bioconversion processes are also extremely sensitive to changes in temperature.
In addition, conventional processes produce biogas that is high in carbon dioxide. Carbon dioxide is a harmful compound to the environment and there is a general objective to get rid of it.